1. Field of the Invention
The invention relates to the handling of an article by means of a robot arm and, more particularly, to the handling of an article by means of a hand of a robot arm while monitoring the location of the hand in order to know the location of the article being handled.
2. Description of the Prior Art
The handling of articles by means of robot arm devices is known. A typical robot arm may include one or more arm elements, e.g., two such arm elements, interconnected by pivotal joints, with the robot arm terminating at one of its ends in a "hand" for supporting an article, and with the robot arm being mounted at its other end, such that the hand may be manipulated between desired positions of the article. Suitable manipulating means for operating the robot arm to move the hand between the desired positions of the article, and suitable control mechanisms, which may be computer-operated, are generally associated with such a robot arm.
In order to control the movements of the robot hand, it is necessary, of course, for the control mechanisms to be informed as to the location of the robot hand at all times. Previously, tracking or monitoring of the position of the robot hand has been accomplished by means of sensors, located at each pivotal joint, for indicating the angle between adjacent arm elements at such pivotal joint. Since the length of each arm element is known, a vector summing operation is relied upon to determine the location of the robot hand and, thus, of the article.
The prior art, robot hand monitoring technique just described presupposes that there is, at most, only a negligible deformation of the set of interconnected arm elements. Any deformation, if more than negligible, would render inaccurate the location determined for the robot hand on the basis of the vector summing operation. The use of the robot hand as an article-supporting and manipulating facility, however, causes the weight of the article to impose a load on each arm element, providing a bending moment which increases with increasing distance of the hand from the arm mounting position during movement of the supported article, and which tends to deform the robot arm configuration. Other loads imposed upon the robot hand, e.g., due to contact of the supported article or the hand with another object, will also tend to deform the arm. Thus, the employment of robot arms has generally been restricted to the handling of only very small and light articles, to operations in which precise article positioning is not important, and/or to usages involving massive robot arm structures, e.g., large castings, for supporting large loads without significant deformation. Any such massive robot arm structures are, of course, relatively costly to produce, manipulate and control, as compared with the relatively light structures which could be employed were not load-caused deformation of the arm elements a source of inaccuracies in the hand location monitoring technique.
Accordingly, it would clearly be advantageous to provide a technique for monitoring the location of a robot hand, in order to know the location of article supported in the hand, wherein the accuracy of the technique is unaffected by any deformation of the robot arm which includes the hand.